Manufacture of mellitic acid



July 22, 1941.

' B. .Jul-:TTNERY MANUFACTURE OF. MELLITIC ACID Filed April' e, 1939 INVENTOR .Bernard `Twezzner ATTORNEYS Patented July 22, 1941 RMNUFACTURE F IWIELLITIC ACD) Bernard Juettner, Pittsburgh, Pa., assignor to Carnegie Institute of Technology of Pittsburgh, Pennsylvania, Pittsburgh, Pa., a corporation of Pennsylvania Application April 6,1939, 'serial No. 266,345

(c1. 26o-52s) Claims.

My invention relates to a process for the production of mellitic acid, and more especially to `a process for manufacturing mellitic acid from carbon compounds, and has for its object to provide a simple, eiicient and inexpensive method by which mellitic acid may be produced. The term-carbon compound is used herein to include only such substances of condensed carbocyclic structure as contain at least one six-membered carbon ring with six other aromatic carbon atoms attached thereto. This application is a continuation-impart of my copending application Serial No. 135,061, led April 5, 1937 (Patent 2,176,348, granted October 1'7, 1939), for an improvement in the Manufacture of mellitic acid. In my said copending patent, I have described a 'method of making mellitic acid from carbonaas alkaline permanganate, sodium hypochlorite,

fuming nitric acid with potassium chlorate, concentrated sulphuric acid, concentrated nitric acid, sodium chlorate and osmium tetroxide, anodic oxidation, fuming nitric acid with vanadium catalyst. 'I'he yields of the pure acid were extremely small and in most cases only crude proucts were obtained. The best yields were reported by H. Meyer and co-workers who oxidized carbon from various sources by refluxing with furning nitric acid and 0.2% vanadic acid. The crude mellitic acid was converted into the ammonium salt and purified through the copper salt. Their yields are based on the crude ammonium salt. The yield of the pure acid is not given, Abut from experiments I have conducted following their procedure, I am forced to conclude that the yields were small. I have also found that their procedure using only fuming nitric acid and vanadium catalyst even for a prolonged oxidation period of two weeks was wholly ineifective with high temperature cokes from various coals. The oxidation stopped at the formation of high molecular intermediate compounds.

I am aware also that attempts have been made to oxidize carbonaceous materials by the use of alkaline permanganate oxidation. This procedure results mainly in oxalic acid being formed with very little mellitic acid, when, for example, low temperature cokes were employed as the starting material. When high temperature cokes were employed as the starting material, it was found that alkaline permanganate had extremely little effect.

I have found that a very satisfactory yield of mellitic acid may be obtained from carbon material by rst treating the material for a suitable period of time with a suitable oxidizing acid, with or without the presence of a catalyst, followed by oxidation with an oxidizing salt such as alkaline permanganate. Mellitic acid obtained by following my method is pure, of excellent quality, and the yield is high.

The principal object of my invention is to provideV a process by which carbon containing material as herein defined may be treated to produce mellitic acid of a high quality and with a good yield. In general, my process consists of reuxing a substance of condensed carbocyclic structure as contain at least one six-membered carbon ring with six other aromatic carbon atoms attached thereto with an excess of an oxidizing acid such as fuming nitric acid, with or Without the presence of a catalyst such as vanadic acid. After prolonged boiling, say, for a period of two weeks, the whole mixture is evaporated to dryness and the residue then oxidized byrboiling for a considerable period of time, say one week, with an excess of an oxidizing salt, in an alkaline solution such as alkaline permanganate, and then ltering. A high yield of mellitic acid of excellent quality may be recovered from the ltrate.

With high temperature cokes and especially graphite, the superiority of the nitric acid-alkaline permanganate oxidation is best illustrated. After boiling Acheson graphite (-200 mesh) with fuming nitric acid and ammonium vanadate for two weeks, no visible change had taken place. The material had still the appearance of graphite. But on subsequent treatment with alkaline permanganate, the graphite was oxidized to mellitic acid. Graphite not pre-oxidized with nitric acid was not perceptibly attacked by alkaline permanganate.

The new procedure using fuming nitric acid and ammonium vanadate was applied to '700 C. vand 1000 C. cokes. Here the nitric acid oxidation proceeded much further than with graphite and intermediate compounds were formed which, on subsequent alkaline permanganate Yields of mellitic acid by thetreatment kwith nitric acid and a catalyst followed by treatment with an dxidieing'salt-per 100 gram material Total acids "Amma a/eleih after electrolnium melered by ysls mate electrolysis J Grams 700 O. Edenbom coke. 39. 7 37.9 24.1 1000 C. Edenborn coke'. 7 w Y '29.4 35.4 22.5 Acheson electrode graphite. 23. 7 30.0 19. l

The mellitic acid was identied by analysis and .by preparing the neutral methyl-ester.

VIn the practice of my invention, the apparatus illustrated in the accompanying drawing may be employed. In the drawing:

y Figurel lis a diagrammatic side elevation of a vessel` suitable .for use in boiling certain mixtures; and -Y Figure 2 is av diagrammatic side elevation of a three-compartment cell suitable for use in this process.v I

In Figure 1 of thedrawing, there is shown an `apparatus which Acan be conveniently used for boiling the mixture during aY certain phase of .theprocess The apparatus consists of an iron vessel I with a removable water-cooled lid kI I, through which lid a shaft I2 with a paddle adjacent the bottom of the vessel passes. This stirring device is driven by a suitable prime mover,vnot shown, A tube I4 passes through the cover YI I-, and a cover I5 is fitted over the outer end of the tube. Through this tube materials `may be introduced into the iron Vessel from time totime. v .v Figure' 2 represents a three-compartment cell comprising a vessel I6 of non-conducting material divided into three'cells by porous membranes I'I, I8, preferably made of parchment. In compartment A, a platinum anode I9 is placed. This is called the anodic compartment. This compartment may be provided with a cooling coil of non-conducting material such asY glass which will not affect or be affected by the liquid `in the anodic compartment. In compartment C, .a hollow A'cathode' 20, formedfrom copper and having pipes 2lv and 22 through whichcooling water is circulated, isplaced. This compartment is k'nownl as thefcathodic compartment. The anode and the cathode are connected to a suitable source c`direct current electricity. The compartmentB is referred to as'the middle compartment. This apparatus is more particularly `described and claimed in the co-p'ending application of Henry C`. Howard, Serial No. 135,038, iled April 5, 1937 (Patent 2,176,343,y granted October 17, 1939). The following examples illustrate the invention.

" Example I Cokevwas formed by heating Edenborn coal to approximately 1000 C. One hundred grams of the coke (-200 mesh), together with 1500 cc. fuming nitric acid (sp. gr. 1.5) to which 0.24 gram ammonium vanadate was added, were reiiuxed for 14 days in an ordinary Pyrex ask With a reux condenser. Then the Whole was evaporated to dryness in a steam bath under a vacuum of approximately 20 mm. of mercury. The solid residue Was dissolved in about 3 liters of water containing 200 grams of potassium hydroxide and transferred to an iron vessel provided with a double-Walled, water-cooled lid with an efficient stirrer in the vessel (see Figure 1). The solution was brought to a boil and sufcient excess potassium permanganate -was introduced from time to time so that the color remained purple during the seven days of boiling. During that time less than grams of potassium permanganate Was used. The excess potassium permanganate was destroyed with formic acid. The manganese dioxide was filtered off and thoroughly washed. The ltrate was concentrated and placed in the middle cell of a three-compartment cell with parchment membranes separating the threecompartment cell (see Figure 2). The anodic and cathodic compartments were lled with distilled water. To obtain good conduction, about 50 cc. formic acid was added to the alkaline ltrate. After electrolysis for four days with a current not exceeding 4 amp. at 110 volts, the acids were found to have migrated to the anode compartment. The cathodic and anodic compartments were emptied and refilled'with distilled water twice during each 24 hours of the electrolysis. The combined anodic solutions were evaporated to about 300 cc. and the mellitic acid was 4precipitated as the ammonium salt by adding the concentrated anodic solution to 1500 cc. of a Well cooled solution of ammonium hydroxide (sp. gr. 0.9). An insoluble precipitate was formed which was found to be pure ammonium mellitate free from oxalic acid or any other impurities,

The yield of the dried salt Was 35.4 grams. After drying for 48 hours over sulphuric acid under a vacuum of about 20 mm. of mercury, the

7 salt had the approximate composition of a hexahydrate. To obtain the free acid, the ammonium mellitate was added to 1000 cc. of distilled Awater containing 50 grams of potassium hydroxide and 12 cc. formic acid` The mixture was Velectrolyzed as described above. The dried residue obtained from the evaporated anodic solutions consisted of 22.5 grams of analytically pure mellitic acid.

Example II One hundred grams of triphenylene- (9-10 benzophenanthrene) was added to 11/2 liters of nitric acid (sp. gr. 1.5) and refluxed for a period of two weeks. The whole was then evaporated to dryness over a steam bath under a vacuum of about 20 mm. of mercury. To the residue, 200 grams of potassium hydroxide dissolved in 3 liters of water was added and the mixture boiled with Iconstant stirring for one week in an iron vessel having a water-cooled lid and an agitator in the vessel (see Figure 1). From time to time during the week, 800 grams of potassium permanganate was added at a rate such that the liquid always showed Ia purple color. The excess of potassium permanganate was destroyed by adding sodium formate (lHCOONa). The MnO2 Was filtered off and washed. The filtrate contained the mellitic acid as a potassium salt. The filtrate was then concentrated by evaporation at atmospheric pressure over a. steam bath to a volume of about 1 liter. TheV ltrate was then placed in the middle compartment of a three-compartment cell with a parchment membrane separating the compartments (see Figure 2). To obtain good conducti-on, about 50 cc. of iormic acid was added to the alkaline filtrate. The -anodic and cathodic compartments were lled With distilled Water. Electrolysis was conducted for 4 days with a current not exceeding 4 amps. at 1110 volts. The cathodic and anodic compartments were emptied and refilled with distilled water twice during each 24 hours.

The combined anodic solutions obtained above were converted to mellitic acid through the ammonium salt as described in Example I. The yield was 67.2 grams.

Example III Five hundred grams Clairt-on coke (-200 mesh) was refluxed for a total period of 3 weeks with 5500 cc. nitric acid (sp. gr. 1.5) and 300 cc. nitric acid (sp. gr. 1.16). The nitric acid was added in portions. First 3000v cc. nitric acid (sp. gr. 1.5) was added. After boiling for a little more than a Week, the volume of the nitric acid had decreased very much, but the color of the mixture was still the initial black. Then 300 cc. of nitric acid (sp. gr. 1.6) was added and boiling continued for 3 days more. The color still remained black. An attempt was made to iilter off the insolubles. This, however, did not Work due to the colloidal nature of the reaction products. Therefore, the oxidation was continued by adding, first 2000 cc. of nitric acid (sp. gr. 1.5) and later 500 cc. of nitric acid (sp. gr. 1.5). After about a Week of further refluxing, the color had changed from black to light brown. It was allowed to cool and the insolubles were separated by sedimentation and filtration. In this case filtration was not difficult. The in-solubles were then -dried and further oxidized with alkaline potassium permanganate. Less than 100 grams of potassium permanganate were used during 6 days. The excess potassium permanganate was destroyed with formic acid. The manganese dioxide was filtered off and washed. The filtrate contained the mellitic acid as a potassium salt. The filtrate was treated as was the filtrate in Example I. The yield of mellitic acid was 71.4 grams.

Example IV Twenty-five grams of d'ecacyclene (trnaphthylene benzene) Cse'Hia supplied by Fraenkel and Landau, was a-dded to 250 cc. of nitric acid, sp. gr. 1.5, at -10 C. The mixture was boiled under reflux for nine days. The whole was evaporated to dryness on the water bath and a residue of 4.6.88 g. obtained. This residue was dissolved in 2 liters :of water containing 60 g. potassium hydroxide. 400 g. potassium permanganate were -consumed in the oxidation over a period of 5 days. The precipitated manganese dioxide was filtered off and the free Iacids recovered by electrolytic decomposition of the fil-trate, 9.12 g. of crude acids being recovered. These -acids were dis-solved in cc. water and the ammonium mellitate precipitated by adding 200 cc. cold ammonium hydroxide, sp. gr. 0.90.

|One mol of the hydrocarbon, 450 g., should furnish one mol of mellitic aci-d, 342 g., on oxidation. Actually, g. of the hydrocarbon yielded 10.5 g. of pure ammonium mellit-ate, equivalent to 6.7 g. mellitic acid, or 35.3% of the theoretical yield.

" It is possible to recover the mellitic acid from the alkaline iiltrate as obtained, for instance, in Example I, through the barium or calcium salt. The alkaline nitrate is made just slightly acidic, for instance with hydrochloric or nitric or acetic acid,y and treated with a soluble barium or calcium salt. The insoluble barium or calcium mellitate is formed. This is filtered off and treated with a suicient amount of dilute sulphuri-c acid and the insoluble barium or calcium sulphates, 'separated by filtration, and the mellitic acid recovered by evaporation of the filtrate.

It is also possible to recover the mellitic acid from the alkaline filtrate as the neutral methyl ester. The alkaline filtrate is evaporated to dryness and treated with an excess of dimethyl sulphate at room temperature for several'days. In this manner, the neutral methyl ester of mellitic acid is formed and the alkali hydroxide is changed to a sulphate. The inorganic matter from the coke, mainly silica, is also present in this mixture. To obtain the ester, the whole mixture is treated with water and the excess dimethyl sulphate is decomposed by adding a bicarbonate. The insoluble material consisting of silica and ester is ltered off `and the ester is obtained by extraction with alcohol or acetone. The ester maybe `purified by recrystallization from a mixture of methyl alcohol and Water.` 'Y

Instead of using dimethyl sulphate for preparing the ester, a mixture of methyl alcohol and sulphuric acid may be employed. The well dried evaporation residue from the alkaline ltrate is suspended in a deiinite volume of methyl alcohol and to this is added carefully about half that volume of concentrated sulphuric acid containing copper sulphate as catalyst. After heating the mixture for one hour at 125 C., it is poured into water when silica and ester separate. `The ester is obtained by extraction as above.

In this method the inconvenient and lengthy operation of decomposing the excess dimethyl sulphate is avoided.

The following table shows the yields in grams of mellitic acid per grams of the following materials (pulverized to approximately -200 mesh) Heated at4 Room temp. 500 C.

Pittsburgh coal 5. 5 11. 9 24. l 22 Illinois No. 6 coal High splint coal. Pocohontas #8 coal Anthracite Cellulose (cotton) Acheson graphite Natural graphite Activated charcoal Pitch from low-temperature tar 9-10-benzophenanthrcnc Petroleum coke The effect of heat treating the carbonaceous material before subjecting it to the process which I have invented is shown in the above table.

It may or may not be desirable to use a catalyst depending upon the conditions of the oxidation. If a large excess of nitric acid is used, the catalyst is of no advantage. If the amount of nitric acid is greatly reduced, the catalyst may be of importance by speeding up the oxidation with nitric acid. However, the yields of mellitic acid are the same whether a catalyst is used or not. But the amount of permanganate required in the second ustage may be reduced by using a catalyst in large excess.

`needed `will be decreased. The most economical lprocess vmust be ascertained experimentally for .each1type of carbon containing material. This data can be readily obtained following the teach- .ings of my invention.

:It is evident that by the process which I have invented, mellitic acid can be produced in any de- -sirable quantities in an economical and expeditious manner.

, While I have specifically describedthe preferred .embodiment of my invention, it is to be understood that the invention may be otherwise practicedwithin the scope of the following claims.

I claim:

`1. In the process of making mellitic acid, the .steps which consist of treating a substance of condensed carbocyclic structure which contains atleast one six-memberedv carbon ring with six other-aromatic carbon atoms attached thereto 'with nitric acid followed 'by a treatment with an alkalimetal permanganate in an alkaline solution.

'27; In the process of making mellitic acid, the steps which consist of treating a substance of `condensed carbocyclic structure which contains at-fleast'one six-membered carbon ring and six Aother aromatic carbon atoms attached thereto uwith nitric acid and a catalyzer followed by a treatment with an alkali metal permanganate in yan lalkaline solution.

3. In the process of making mellitic acid from .a `substance of condensed carbocyclic structure whichcontains at least one six-membered carbon ring with six other aromatic carbon atoms attached-thereto, the steps which consist of heating thesubstance, refluxing the material with an excessof an oxidizing acid, evaporating the mixture to dryness, dissolving the residue in an aqueous solution of potassium hydroxide and boiling the 'solution with an excess of potassium per- `=manganate.

4. In the process of making mellitic acid from a substance of condensed oarbocyclic structure which contains at least one six-membered carbon ring with six other aromatic carbon atoms attached thereto, the steps which consist of heating the substance, reuxing the material with an excess of an oxidizing acid, evaporating the mix'- Vture to dryness, dissolving the residue in an aqueous solution of a metallic hydroxide andH boiling the solution with an excess of an alkali metal permanganate.

5. In the process of making mellitic acid, the steps which consist of treating a substance of condensed carbocyclic' structure which contains at least-one six-membered carbon ring with six other aromatic carbon atomsrattached thereto withnitric acid followed by a treatment with potassium permanganate iny an alkaline solution of potassium hydroxide.

6. In the process of making 'mellitic acid by treating a substance oi condensed carbocyclic structure which contains at least one six-membered carbon ringwith six other aromatic carbon atoms attached thereto' with Ean oxidizing acid, the step of treating the products thus obtained with a solution of an alkali metal permanganate and an alkali metal hydroxide.

7. In the process of making mellitic acid by treating a' substance of condensed carbocyclic structure which contains at least one six-membered'carbonV ring with six other aromatic'carbon atoms attached thereto with fuming' nitric acid, the step of treating the product thus formed with an alkali metalpermanganate in an alkaline solution,

8. In the process of making; mellitic acid by treating a substance of condensed carbocyclic structure which contains at least vone six-membered carbon ring with six other aromatic carbon atoms attached thereto with nitric `acid, the step of treating the insoluble residue thus'obtained with a solution of an alkali metal hydroxide and an alkali metal permanganate.

9. In the process of making mellitic acid by treating a substance of condensed carbocyclic structure which contains at least one six-membered carbon ring with six other aromatic carbon atoms attached thereto with an oxidizing acid, the steps of drying the residue and then treating the residue with a solution of an alkali metal hydroxide and an alkali metal permanganate.

10. In the process of making mellitic acid from a substance of condensed carbocyclic structure which contains'at least one six-membered carbon ganate.

BERNARD JUETTNER. 

